CHEMICAL FINGERPRINTS OF HYDROLOGICAL COMPARTMENTS AND FLOW PATHS AT LA CUENCA, WESTERN AMAZONIA

A forested first-order catchment in western Amazonia was monitored for 2 years to determine the chemical fingerprints of precipitation, thro ughfall, overland flow, pipe flow, soil water, groundwater, and stream flow. We used five tracers (hydrogen, calcium, magnesium, potassium, a nd silica) to distinguish ''fast'' flow paths mainly influenced by the biological subsystem from ''slow'' flow paths in the geochemical subs ystem. The former comprise throughfall, overland flow, and pipe flow a nd are characterized by a high potassium/silica ratio; the latter are represented by soil water and groundwater, which have a low potassium/ silica ratio. Soil water and groundwater differ with respect to calciu m and magnesium. The groundwater-controlled streamflow chemistry is st rongly modified by contributions from fast flow paths during precipita tion events. The high potassium/silica ratio of these flow paths sugge sts that the storm flow response at La Cuenca is dominated by event wa ter.